1. Field of the Invention
The present invention provides two part, room-temperature curable epoxy resin/(meth)acrylate compositions. The compositions provide among other advantageous properties high flash point and low odor, and reaction products thereof demonstrate comparable and often improved fixture time, improved adhesion strength, and improved adhesion strength over time, to substrates which are ordinarily difficult to bond (such as plastics) with epoxy-based compositions, as contrasted to commercially available comparable products that are of low flash point and higher odor.
2. Brief Description of Related Technology
Two-part epoxy resin compositions are known. See e.g., U.S. Pat. No. 4,668,736 (Robins). Such compositions are formulated in a two-part manner so as to allow the system to be reactive at room temperature when the two parts are mixed together. Ordinarily, in one of the parts there is provided an epoxy resin and in the other of the parts there is provided a hardener. To one or the other of the parts may be included additional materials to alter the physical properties of either part individually or when mixed together in its uncured state, or of the cured reaction product.
Acrylic-based adhesive compositions are well known. See e.g., U.S. Pat. No. 4,536,546 (Briggs). While adhesives based on this technology appear to have been sold under the tradenames PLEXUS MA 300 and 310 by Illinois Tool Works Inc., Chicago, Ill., they oftentimes exhibit an obnoxious odor and/or have high toxicity, causing in some end users a reluctance to use them. In addition, these adhesives possess a low flash point—meaning they are flammable—causing enhanced safety concerns to distributors, transporters and end users. Moreover, while the adhesives may provide adequate dry to touch time and fixture time, improvements of such properties would be desirable.
Two-part epoxy resin compositions are also known, where one of the parts includes an acrylic-based adhesive. For instance, U.S. Pat. No. 4,426,243 (Briggs) describes an adhesive composition that is prepared from two different adhesive materials—one being an epoxy resin and the other an acrylate-based adhesive—, being chemically bonded together by a bifunctional component having as one of its functional groups an epoxy and as the other an acrylate. See also U.K. Patent No. GB 2166447B.
In addition, International Publication No. PCT/US98/12260 discloses a polymerizable composition for use with an aerobic initiator that is based on ethylenically unsaturated monomers, such as (meth)acrylates, which have a boiling point of at least 160° C., an average monomer fluorophilicity of at about 3.25, and polymers thereof have a glass transition state of at least −20° C. These compositions are said to be useful in bonding low surface energy substrates.
Accordingly, it would be desirable to provide the benefits of both an epoxy resin-based adhesive and an acrylate-based adhesive without many of the perceived detriments to either of these adhesive types, or those adhesives using a combination of those chemistries. For instance, oftentimes industrial end users of such adhesives, for instance acrylate-based adhesives, have commented that commercially available adhesive compositions possess an obnoxious odor, contain highly toxic constituents, and/or possess flash points that make using the adhesives particularly cumbersome or unattractive because of safety issues. In addition, in their cured state (or reaching the cured state), industrial end users have commented that the commercially available adhesive compositions, such as epoxy-based adhesives, do not reach a significant fixture strength in a rapid enough time period. End user perception in this regard has in part provided an obstacle to the continued growth of the market of such adhesives.
There, therefore, is deemed to be a need for epoxy-based compositions that address the marketplace issues identified above.